A row crop harvesting machine such as a corn harvesting machine described for example in U.S. Pat. No. 6,237,314, U.S. Pat. No. 4,244,162 and DE 10 2004 061 112 has a header displaceable along the ground which comprises a plurality of grooves each adapted to receive a row of corn stalks during operation of the harvester. A conveyor chain, having its longitudinal axis parallel to the grooves of the header and spanned over a drive sprocket and an idler sprocket, is generally provided at each of the grooves to convey the harvested material, such as corn ears or grain, towards a central gathering point in the corn harvester.
In the known corn harvesting headers, tension in the conveyor chains is maintained by changing the axial distance between the drive sprocket and the idler sprocket by means of a spring system, which pushes the idler sprocket away from the drive sprocket when the tension in the conveyor chain is too low, and pulls the idler sprocket towards the drive sprocket when the tension in the chain is too high. The idler sprocket is thereby guided in a direction parallel to the grooves of the corn harvesting header, using linear guidance elements which obstruct movement of the idler sprockets in the cross direction. In U.S. Pat. No. 6,237,314 and in DE 10 2004 061 112, for example, the idler sprocket is connected to the spring system by means of a connecting arm which slides through a recess, wherein the recess supports the linear movement of the idler sprocket in a direction away from or towards the drive sprocket.
The use of linear guidance elements, however, has several disadvantages, since during operation of the corn harvester dirt and corn waste can become jammed between the guidance elements, thereby blocking the functioning of the chain tensioner. Moreover, the guidance elements are difficult to maintain and are prone to blocking due to rust formation during periods of inactivity of the corn harvester.